This invention relates to distillation equipment and processing, specifically an improved design for a vapor compression distillation apparatus and method.
Vapor compression distillation has the potential to provide significant savings in capital and operating costs over single or multiple effect evaporators not using this technology. Vapor compression distillation is typically limited in application by economics and operational problems.
Vapor compression distillers of various designs have been proposed for many years. Most of these designs have seen little or no commercial use due to both functional problems and for economic reasons. The commercial feasibility for these previous designs is strongly affected by many factors. The exact disadvantages of earlier designs are varied and include poor heat transfer, fouling tendencies, poor or inflexible application of makeup heat for thermal losses, poor equipment reliability, higher operating costs, inflexibility in liquid flows, higher maintenance costs, higher initial capital costs, difficulty in system startup, and lack of flexibility in processing capacity.
Briefly described, the invention is vapor compression distillation apparatus and process. A liquid is circulated through an evaporation loop comprising an evaporation vessel in fluid communication with a first side of a primary heat exchanger. The liquid is boiled to produce a vapor. The vapor is passed through a vapor compressor to a second side of the primary heat exchanger so as to condense at least a portion of said vapor. Additional amounts of the liquid are introduced at a feed rate so as to maintain approximately the same volume of liquid in the evaporation loop. The liquid is recirculated at a recirculation rate of 25 to 200 times the feed rate.
The invention is also a two-loop vapor compression distiller. The major components of the invention are a primary heat exchanger having a first side thereof which facilitates heat flow to a second side thereof, an evaporation vessel for boiling a liquid and collecting the vapor of the liquid in the upper portion of the evaporation vessel, a vapor compressor communicating with the upper portion of the evaporation vessel and with an inlet to the first side of the primary heat exchanger, and a recirculation pump. There is also an evaporation loop providing fluid communication from the evaporation vessel through the recirculation pump and through the second side of the primary heat exchanger and back to the evaporation vessel, a means for boiling the liquid within the evaporation loop, a transfer line for supplying the liquid to the evaporation loop at a feed rate, a secondary heat exchanger having a first side thereof which facilitates heat flow to a second side thereof, a condensate line for providing fluid communication between an outlet of the first side of the primary heat exchanger and an inlet of the first side of the secondary heat exchanger, a feed pump, a feed loop providing fluid communication from the feed pump through the second side of the secondary heat exchanger to the transfer line and back to the feed pump, and a feed line for supplying the liquid at the feed rate to the feed loop.
Accordingly, several objects and advantages of the invention are to provide a vapor compression distiller which addresses the disadvantages of prior vapor compression distillers. These include improved heat transfer by rapid turbulent flow of liquid through the inside of the heat exchanger provided by one or more high volume recirculation pumps, and optionally the use of turbulence enhancing devices (turbulators) inside the heat exchanger which increases the liquid turbulence at the inside walls and dramatically reduces or stops fouling, increased flexibility of addition of makeup heat by providing for the addition of steam to compensate for thermal losses in either the recirculating liquid, the heat exchanger, or the vessel, as well as use of a heat exchanger between the condensate liquid and the feed liquid to recover heat from the hot condensate. Variable system feed rates are addressed by use of a system idle function which allows the system to maintain operating temperatures and rapidly and automatically continue operation when the system feed again resumes. This simple, reliable design allows for easier system operation and reduced maintenance, as well as reduced time required for cleaning of the heat exchanger in high fouling environments.
Still further objects and advantages will become apparent from a consideration of the ensuing description and accompanying drawings.